shape op• Data kinds: image2d → image2d
• Call: import fullseye as fs; fs.ledger.arc(img, center, radius, start_deg, end_deg, color='neutral', width=2, alpha=1.0, scheme='okabe_ito') (to call the implementation directly, import annotate; annotate.arc(img, center, radius, start_deg, end_deg, color='neutral', width=2, alpha=1.0, scheme='okabe_ito'); from the registry, opsannotate.get("arc"))
A circular arc. Angles are in degrees, clockwise from the screen x-axis (because row points down).
ValueError
radius not positive, angle non-finite, start == end, alpha outside [0,1].
Drawing: paints pixels whose distance d from the centre satisfies |d - radius| <= max(0.6, width/2) and whose azimuth lies in the range (end_deg - start_deg) mod 360 clockwise from start_deg (no anti-aliasing). The azimuth is atan2(y - cy, x - cx), with 0 degrees = right (+x), 90 degrees = down (+y), clockwise positive.
• center: (x, y), x = column, y = row. May be outside the image (overhang is simply cut off).
• radius: positive [px].
• start_deg, end_deg: degrees. Drawn clockwise from start to end. A difference that is a multiple of 360 (end - start not 0 but e.g. 360) is a full circle. start == end is "length 0", hence ValueError.
• width: line width [px]. max(0.6, width/2) is used as the half-width, so even below 1 px it does not break up.
• img / color / alpha / scheme are handled as in rounded_rect (float64 copy, [0, 1], role name or RGB).
• Return value: float64 of the same shape as the input.
For the conventions of academic figures that write angles in, annotate_angle takes care of everything down to the leader text.
• figure_annotation family guide
• dataset_conventions — Training-dataset conventions — COCO / YOLO / VOC and pitfalls in visual inspection
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
• annotate_gallery — py -3.11 examples/annotate_gallery.py
• poc_polish_wipe_measure — py -3.11 examples/poc_polish_wipe_measure.py
• poc_weld_radiograph_porosity — py -3.11 examples/poc_weld_radiograph_porosity.py
image2d as input)text_box · arrow · leader_line · label_points · crosshair · legend_box · color_bar · scale_bar
shape)rounded_rect · filled_polygon · ellipse
*Provenance: annotate.py — ANNOTATE operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.